Emit biblio.json during build so downstream proposals can build on this one

Add --write-biblio build/biblio.json to the ecmarkup invocation, and set
the spec's location metadata so biblio entries resolve to absolute URLs.
Since the existing publish workflow deploys the build/ directory to
gh-pages, the biblio will be available at
https://tc39.es/proposal-fma/biblio.json for other proposals to load
via ecmarkup's --load-biblio.

Author: jessealama

package.json

@@ -5,7 +5,7 @@
   "scripts": {
     "start": "npm run build-loose -- --watch",
     "build": "npm run build-loose -- --strict",
-    "build-loose": "node -e 'fs.mkdirSync(\"build\", { recursive: true })' && ecmarkup --load-biblio @tc39/ecma262-biblio --verbose spec.emu build/index.html --lint-spec"
+    "build-loose": "node -e 'fs.mkdirSync(\"build\", { recursive: true })' && ecmarkup --load-biblio @tc39/ecma262-biblio --write-biblio build/biblio.json --verbose spec.emu build/index.html --lint-spec"
   },
   "homepage": "https://github.com/tc39/template-for-proposals#readme",
   "repository": {

spec.emu

@@ -7,6 +7,7 @@
 title: Fused Multiply Add
 stage: 2
 contributors: Waldemar Horwat
+location: https://tc39.es/proposal-fma/
 </pre>
 
 <emu-clause id="sec-fmamultiply" type="abstract operation">